1. Field of the Invention
The present invention relates to a self-tuning apparatus of vehicle speed pulse coefficient and a method thereof configured to self-tune a value of vehicle speed pulse coefficient converting the number of vehicle pulse signals generated in the course of a traveling mobile object to a traveling distance and a traveling speed.
2. Description of the Related Art
Generally, driving wheels of a mobile object are equipped with vehicle speed sensors such as differential odometers and the like. The differential odometer generates a number of vehicle speed pulse signals in proportion to a traveling distance of a mobile object, such that multiplication of the number of vehicle speed pulse signals generated by the vehicle speed sensor with vehicle speed pulse coefficients can compute a traveled distance of the mobile object.
Furthermore, when the number of vehicle speed pulse signals generated for each unit time by a vehicle speed sensor is counted, the number of vehicle speed pulse signals counted per unit time multiplied by the vehicle speed pulse coefficients can compute a traveling speed of a mobile object.
Even if a mobile object travels a predetermined distance, the number of vehicle speed pulse signals generated by a vehicle speed sensor is not the same. For example, frictions between vehicle wheels and roads are differently generated in relation to a case where a mobile object travels on a high way and a road, and a traveling speed of the mobile object. Furthermore, frictions generated between vehicle wheels and roads differ when a vehicle travels on a road on a rainy or snowy situation. Even if a mobile object travels a same distance, the number of generated vehicle speed pulse signals differ due to differently generated frictions. Meanwhile, there are generated frictions on the vehicle wheels according as a mobile object travels, and the number of vehicle speed pulse signals are differently generated in response to the amount of generated abrasion.
Preferably, a vehicle speed pulse coefficient value is flexibly adjusted in response to road environments and the state of a mobile object including frictions generated between the vehicle wheels and a road and an abraded state of vehicle wheels, and the like.
The vehicle speed pulse coefficient is generally fixed beforehand at a predetermined value when a mobile object is outputted from a motor factory. The vehicle speed pulse coefficient value may be periodically tuned at a maintenance shop of a mobile object. However, the afore-mentioned vehicle speed pulse coefficient is tuned at a value under a predetermined tuning environment, such that it was not flexibly tuned in response to spontaneously variable road environment changes and current state of a mobile object as the mobile object travels along. As a result, there have occurred lots of errors when the traveling distance and traveling speed are computed by the number of the vehicle speed pulse signals.
Generally, a navigation system is such that at least four or more navigation messages are received by a Global Positioning System (GPS) receiver out of navigation messages periodically transmitted by a plurality of GPS satellites arranged on geostationary orbits over the Earth to detect 3D location coordinates. The location coordinates detected by the GPS receiver are determined as a current location of a mobile object, and the detected current location of the mobile object is map-matched on a digital map so that the digital map and the location of the mobile object can be displayed on a display screen.
In a navigation system using GPS, the current location of the mobile object detected by the received navigation messages can be accurately detected only at an area where the GPS receiver can precisely receive the navigation messages, and the current location of the mobile object cannot be accurately detected at an area where the navigation messages cannot be precisely received. In other words, in the navigation system using the GPS, navigation messages transmitted by the plurality of GPS satellites are received by a GPS receiver to detect the location of a mobile object. Therefore, the receiver may not detect coordinates of a vehicle location or merely can obtain very incorrect results of detection of the coordinates at areas, including the interiors of tunnels thickly-wooded forests or downtown areas surrounded by skyscrapers, where the GPS receiver cannot correctly receive the navigation messages transmitted by the GPS satellites due to the cutoff of GPS signals. Worse yet, the GPS receiver can produce a geometrical error in response to received locations of the navigation messages from the GPS satellites transmitting the navigation messages used for detecting the location coordinates.
The GPS receiver also calculates a Dilution of Precision (DOP) value for discriminating credibility relative to the detected location of the coordinates when the location coordinates are detected by the navigation messages. The DOP value comes to have a lower value as the credibility of location coordinates detected by the navigation messages gets higher, and the navigation system compares with a threshold predetermined by the DOP value to discriminate whether to use the credibility of the location coordinates.
If the DOP value is less than the predetermined threshold, the navigation system discriminates that the location coordinates detected by the navigation messages received by the GPS receiver is credible, and the location coordinates detected by the GPS receiver are determined as a current location of a mobile object.
Furthermore, if the DOP value is not less than the predetermined threshold, the location coordinates detected by the navigation messages are discriminated as discreditable, and the location coordinates detected by the GPS receiver are not used. Instead, the mobile object detects the current location using signals detected by sensors mounted at the mobile object.
A mobile object is mounted with vehicle sensors generating vehicle speed pulse signals in response to rotations of the driving wheels, gyroscopes detecting travel angle variations of the mobile object, and gradient sensors detecting horizontal and vertical gradients of a road on which a mobile object travels. The navigation system uses signals detected by the vehicle sensors, gyroscopes and gradient sensors mounted on a vehicle to measure travel distances and travel directions of the mobile object, which in turn estimate the location of the mobile object.
However, in the prior art thus explained, a vehicle speed pulse coefficient value is not tuned in response to road environments and current state of a mobile object, and instead fixed by any one value thereof such that lots of errors occur with regard to calculated travel distances if the number of vehicle speed pulse signals produced by the vehicle sensors in response to the traveling of the mobile object are calculated as travel distances of the mobile object.
As a result, there is a problem in the prior art thus described in that in case a DOP value is equal to or greater than the threshold in the navigation system, and signals detected by the sensors are used for detecting a current location of a mobile object, a precise location of the mobile object cannot be map-matched, and instead map-matched to a different location to thereby decrease the credibility of the navigation system.